Push back storage assembly

ABSTRACT

A tunnel stand bearing arrangement includes a plurality of shelf channels. Each shelf channel is provided with a circulating conveyor, on which the goods to be stored are received in a frictional manner. Each shelf channel is provided with a stationary slide member located in its end region where the goods are unloaded. The slide member has an active length corresponding to 0.8 to 1.2 times the mean brakeless run-out distance of the conveyor set in motion by the removal of goods. The conveyor is designed such that the non-positive frictional coupling between the conveyor and the goods stored thereon is released in front of the active portion of the slide member.

The present invention refers to a tunnel stand bearing arrangement.

Tunnel stand bearing arrangements of the kind referred to herein aboveare useful for receiving and storing a plurality of goods which areloaded consecutively into the particular shelf channels of the storageassembly, whereby the shelf channels are designed in the kind oftunnels.

As conveyor means for the goods to be stored, usually received onpallets, one may use chain conveyors which are mounted in all the shelfchannels. Such a chain conveyor is disclosed, for example, in thepublication WO 94/00370. In this particular chain conveyor, a conveyingchain equipped with a plurality of rollers is used as the real conveyingmember. Both ends of that conveyor chain are connected to each other toform thereby an endless loop which may be moved along the longitudinalextension of the particular shelf channel. During the loading operation,a pallet is laid onto the conveyor chain and pushed into the shelfchannel by means of a suitable vehicle, e.g. a fork lift truck. Duringthe unloading operation, the pallets are removed from the shelf channelat the same side thereof, again by means of e.g. a fork lift truck.

One difficulty observed in connection with such chain conveyors may beseen in the challenge that the rolling friction of the chain runningalong a supporting rail must be kept as low as possible, since aparticular shelf channel may receive up to twenty pallets and since notonly the individual pallet to be removed from and loaded into the shelfchannel, respectively, has to be moved during the unloading and loadingoperation, respectively, but in each case the entire mass present in theshelf channel. Such moving operation must be performed as quickly aspossible.

Moreover, the total mass of goods, which can amount up to 20-times themass of an individual pallet, has to be slowed down within quite a shorttime after it has been displaced. In most cases, it is essential thatsuch deceleration must be performed without shocks and reliably withinthe overall stopping distance allowed by the geometry of the shelfchannel. This can be realized such that the backward rolling fork lifttrucks after having pulled a pallet out of the shelf channel, stops therow of pallets remaining in the shelf channel at the desired position.However, such an operation is strictly dependent of the skill of thedriver of the fork lift truck. If the driver does not decelerate enoughthe moving pallet row, there is a risk that the pallets overrun the endof the shelf channel whereby the front most pallet falls out of theshelf channel.

The same problems may be observed not only in connection with shelfchannels equipped with chain conveyors, but also in connection withshelf channels of a tunnel stand bearing arrangement provided withdifferent kinds of conveying systems, e.g. roller conveyors whoserollers are interconnected by chains, or trolleys coupled to each other.

In order to find a solution for these problems, a great number of stopand braking systems for continuous shelf storage assemblies has beendisclosed in the prior art; this fact may be an evidence that the aforementioned problem really has not been solved satisfactorily up to now.For example, in the publication mentioned herein before, claim 35discloses such a stop member which has, however, the disadvantagesdiscussed herein after.

For stopping rows of pallets which may have widely varying total massesat a predetermined standstill point, it would be necessary to positivelyaffix a mass-independent path-velocity-curve to the moving total mass.This could be realized with the help of controlled braking motors;however, this would be much too lavish and costly, because each shelfchannel had to be equipped with such a braking system.

Instead, as an obvious and commercially reasonable solution, elasticallydeformeable buffer members are used in most cases. These buffer members,however, perfectly fit in each case a predetermined mass, but show amore or less disadvantageous behavior when the mass is lower or higherthan that predetermined mass. On the other side, the removing velocityis predictable within quite narrow limits due to the knowncharacteristics of the vehicle used for this purpose.

Simple rough estimates for the bandwidth of the required workconsumption for the total mass of the goods present in a shelf channelshow a relation of 1 to 400. The reason therefore is that not only thenumber of pallets present in a shelf channel, but also their particulargross weight may be very different from case to case. Thus, even overrunbrake means equipped with friction linings and/or friction rollerscannot meet the requirements; such means are based on wrong and notpredictable, respectively, physical assumptions.

If the braking systems are not sufficient, the unloading time requiredfor one pallet is increased in the same degree as the transferperformance per time unit is decreased. Moreover, overrun brake meansand elastically deformeable buffers have the disadvantage, common to allsystems disclosed in the art up to now, that the provision thereof inthe shelf channel consumes a valuable portion of the usable length ofthe shelf channel that is not available e.g. in the case of themodification of an existing tunnel stand bearing arrangement. Thus, ineach shelf channel, one pallet storage space would be lost.

It is therefore an object of the invention to improve a tunnel standbearing arrangement in such a way that the conveying means put intomotion by the unloading operation of goods gently and reliably comes toa standstill, independently of the mass put thereon, that any danger isavoided that goods received in the shelf channel overrun the end thereofand may fall out of the shelf channel, even if the operator removinggoods from the shelf channel is not very skilled, and that the length ofthe shelf channel may be used for the storage of goods as completely aspossible, all this without involving commercially intolerable highcosts.

Thus, the invention assumes that the particular conveyor and theconveying member, respectively, is mounted horizontally and that thegoods are received on pallets. During the removal of the pallet from theshelf channel, a non-positive frictional connection between pallet andconveying member is present as long as the pallet to be removed iscompletely pulled away from the conveying member. Thereby, the conveyingmember and, therewith, all pallets remaining thereon are simultaneouslymoved towards the unloading end of the shelf channel when the front mostpallet is pulled out.

For moving the conveying member, a tractive force is required which isequal to the sum of all frictional forces occurring in the conveyor, forinstance the frictional forces of a roller chain moving along asupporting rail. This tractive force can be calculated using thecoefficient of friction, that is quite low and constant within narrowlimits due to the inherent design of a roller chain which may beequipped with roller bearings, multiplied by the total weight of thepallets that is not known and may vary within wide limits. Thecoefficient of friction cannot fall short of a physical minimal value.Would it be zero, --that would be equal to a perpetuum mobile--, theshelf channel had to be arranged not horizontally, but with a gradientof 1% toward the unloading end.

As soon as the tractive force is removed, the conveying member with thepallets loaded thereon slows down and is decelerated along a certaindistance. The deceleration distance can be calculated as thespeed-dependent kinetic energy divided by the consumption of work perdistance unit. Both in the dividend and the divisor of the applicableformula, the same, varying and in the particular case unknown mass iscontained and, thus, can be canceled. Arithmetically, this can beillustrated as follows:

From the formula

    1/2·M·v.sup.2 =M·s·g·Q

follows

    v.sup.2 =2·s·g·Q

or

    s=v.sup.2 /2·g·Q.

Thereby,

v means the velocity in m/sec;

s means the run-out distance in m;

g means the gravitational acceleration in m/s2; and

Q means the coefficient of friction (non-dimensional number in theregion of 0.01).

The following table shows some examples of the practice:

    ______________________________________    Pull-out speed of the pallet in                    0.1     0.15    0.18 0.2  0.3    m/sec    Run-out distance (calculated)                    0.05    0.1125  0.162                                         0.2  0.45    in m    Run-out path minus width of the                    0       0.0125  0.062                                         0.1  0.35    pallet base panel    Application     Seldom  Usual   Usual                                         Usual                                              Limit    ______________________________________

It can be seen from the above calculations that the length of therun-out path is not dependent of the variable mass, but only of thecoefficient of friction of the roller chain and the pull-out speed. Inthe case of roller chain having the rollers mounted by means of rollingcontact bearings, the coefficients of friction are close to each other.In the above table, lower limit values are assumed to demonstrate theworst case.

The top speed of the conveying member is given by the driving speed ofthe backwardly moving fork lift truck during the removal of a palletfrom the shelf channel. Many observations have shown that the speedusually does not exceed 30 cm/sec=18 m/min due to technical reasons.

The basic idea of the invention is based on the consideration, not toprovide additional braking means engaging the pallet mass, but to allowthe pallet to run out, decelerated only by the inherent friction. Forthis purpose, a stationary slide member is located in the region of theunloading end of the shelf channel, having a top surface with an activelength corresponding to 0.8- to 11.2-times of the mean brakeless run-outdistance of the conveying member set in motion by the removal of goodsreceived on the top of the conveying member. In order to release thenon-positive frictional coupling between the conveying member and thegoods resting on its top surface when the goods are unloaded from theshelf channel, the conveying member is designed such that thenon-positive frictional coupling is released in front of the activesurface of the slide member. The result is that the entire active lengthof the slide member can be used for the deceleration of the conveyingmember and, therewith, the goods placed thereon.

The slide member itself does not need to be designed as to beparticularly work consuming. A friction lining would not contribute verymuch to the deceleration, because only appr. one third of the weight ofthe front most pallet, i.e. in the borderline case only 1/60 of thetotal mass received on the conveying member, rests on the slide member.It follows from this that no considerable braking effect is performed bythe provision of the slide member. However, at the end of the run-outpath, a positive stop member can be provided as an additional measure ofsafety, which operates only when the speed of the front most pallet hasbeen considerably reduced.

According to a preferred embodiment, the conveyor is provided with adeflection assembly adapted to deviate the movable conveying member andlocated in the region of the unloading end of the shelf channel in adistance from the unloading end which corresponds at least approximatelyto the active length of the slide member. The backward offset of thisdeflection assembly, however, presents the disadvantage that the rollerchains are not visible by the driver of the fork lift truck. Thus, thepossibility is removed to recognize the beginning and the end of theusable chain run, e.g. by a different color. In order to overcome thisdisadvantage, a further preferred embodiment of the invention providesposition indicator members that are slidably mounted and operated bydriving dog members provided on the conveying member. In this way, theposition indicator members can be displaced between a rest position andan operating position, in which latter the position indicator membersare visible for the driver of the fork lift truck. By means of thesepreferably colored position indicator members, the beginning and the endof the usable chain run can be recognized from a position at the frontend of the shelf channel.

In the following, an embodiment of the invention will be furtherdescribed, with reference to the accompanying drawings, in which:

FIG. 1a shows a schematic side view of the end region of an individualshelf channel of a tunnel stand bearing arrangement;

FIG. 1b shows a view corresponding to the one of FIG. 1a, in a firstphase of operation during the removal of a pallet;

FIG. 1c shows a view corresponding to the one of FIG. 1a, in a secondphase of operation during the removal of a pallet;

FIG. 1d shows a view corresponding to the one of FIG. 1a, in a thirdphase of operation during the removal of a pallet;

FIG. 2 shows an enlarged, more detailed view of the conveying means inthe region of its deflection; and

FIG. 3 shows a schematic perspective view of the slide member, togetherwith a portion of the supporting rail.

In the following, and with reference to FIG. 1a, the general layout of atunnel stand bearing arrangement shall be further explained. In view ofthe fact that such tunnel stand bearing arrangements are well known inthe art, the following explanations only refer to the characteristicswhich are essential for the invention, whereby it is assumed that atunnel stand bearing arrangement is used in which the goods are loadedinto the shelf channel and removed from the shelf channel, respectively,at the same end of the channel, in the present example at the left handside.

FIG. 1a shows a schematic side view of the end region of an individualshelf channel of the tunnel stand bearing arrangement. There is provideda roller chain assembly serving as the conveying means 2. Thereby, it isunderstood that each shelf channel comprises a pair of roller chainslocated in spaced relationship and extending along the shelf channel.Since the conveying means 2 has to receive goods only on its upper side,it is sufficient to design only about one half of the endless travelingconveying means 2 as a roller chain and to interconnect its two free endby e.g. a belt; such a design is lighter in weight and less expensive tomanufacture.

To support the conveying means 2, the shelf channels of the tunnel standbearing arrangement are provided with a cross bar member, designated byreference numeral 20 in FIG. 1a.

In order to deflect the roller chain 2, there is provided a deflectionassembly 3 such that the roller chain is divided into an upper run 2Band a lower run 2C. Moreover, there is provided a support rail member 6which serves to support the upper run 2B of the roller chain 2; thedesign of the support rail member 6 will be further explained hereinafter with reference to FIGS. 2 and 3.

In the region of the end of the shelf channel, there is provided astationary slide member 5 which serves as a run-out zone for the goods15, 15A, 16, 16A, 17, 17A received on the top of the roller chain 2. Asexplained herein before, the length of the running-out zone isindependent of the total mass of the goods 15, 15A, 16, 16A, 17, 17Astored in the particular shelf channel and received on the top of theroller chain 2, because essentially only the conveying speed of thegoods and the roller chain 2, respectively, is to be considered asvariable item.

The active length a of the slide member 5 amounts to approximately 0.8-to 1.2-times of the mean brakeless run-out distance of the conveyingmeans 2 set in motion by the removal of goods 15, 15A, 16, 16A, 17, 17Areceived on the top of the conveying means 2. Thereby, the expression"active length" shall be understood as the length a of the slide member5 between the end of the conveying means 2 and the leftmost end of theparticular shelf channel. Tests performed by the inventor have shownthat the active length a of the slide member 5 amounts, in practice, tobetween 10 and 40 cm. The provision of such a slide member 5 results inthe fact that the length of the particular shelf channel available forthe storing of goods is longer than the effective conveying path of theconveying means 2.

FIG. 1b shows a schematic side view of the end region of an individualshelf channel of a tunnel stand bearing arrangement in a first phase ofoperation during the removal of the front most pallet 15. For thispurpose, as shown in the drawing, a fork lift truck can be used; forsimplicity's sake, only the forks G of the fork lift truck are shown inFIG. 1b to 1d. Preferably, the top surface of the forks of the fork lifttruck is provided with a high friction lining or some sort of drivingdog means as is well known in the art. In order to remove a pallet 15from the shelf channel, the forks G are introduced under the front mostpallet 15 and lifted to such an extent that the high friction lining ordriving dog means provided on the top surface of the forks come intogood non-positive or frictional contact with the pallet 15 to beremoved, but without lifting the rearmost panel of the pallet 15 off theconveying means 2 and without releasing the frictional contact betweenthe pallet 15 and the conveying means 2, respectively.

Thereafter, the operator of the fork lift truck drives his vehiclebackwards and thereby pulls out the front most pallet 15, together withthe conveying means 2 and the further pallets 16, 17 . . . restingthereon. As soon as the fork lift truck and, therewith, its forks aremoved backwards to such an extent that the rearmost bottom panel of thefront most pallet 15 has left the conveying means, as shown in FIG. 1c,the pulling force coupling between fork lift truck and front most pallet15, respectively, and conveying means 2 is geometrically released, withthe result that the pallets 16, 17 . . . still resting on the conveyingmeans are not pulled out any longer, but move towards the end of theshelf channel under the influence of their kinetic energy.

Thereby, the rolling friction acts contrary to the moving total mass,comprising the conveying means 2 and the pallets 16, 17 . . . restingthereon, and decelerates this mass until it comes to a standstill,whereby the front most bottom panel of the pallet 16 remaining on thesurface of the conveying means 2 overruns the end of the conveying means2 and is pushed onto the slide member 5 situated at the end of theconveying means; this situation is shown in FIG. 1d.

The length of the rolling out path is a function of the frictioncoefficient of the conveying means 2 and the pulling out velocity of thepallets, but is independent from the total mass of the pallets 16, 17 .. . still remaining in the shelf channel. As previously mentioned, thelength of the slide member 5 amounts to 10-40 cm in practice; that meansthat the conveying means 2 can have an initial velocity of up to 0.3m/s, supposing a friction coefficient of 0.01, without the risk that thefront most pallet overruns the end of the shelf channel of the tunnelstand bearing arrangement. In order to be on the very safe side, anadditional stop member can be provided at the end of the slide member 5.

The removed pallet 15 is pulled out further by means of the fork lifttruck with a constant velocity and driven away. Thereby, the fork lifttruck already has moved away from the end of the shelf channel of thetunnel stand bearing arrangement, when the running out process of thepallets 16, 17 . . . remaining in the shelf channel has come to an end.

FIG. 2 shows an enlarged, more detailed view of the conveying means 2 inthe region of its deflection assembly 3. In this figure, it can beclearly seen that the conveying means 2 comprises a roller chainassembly, whereby the particular chain link members 2A are provided withjagged projections 4 located on their tops. These jagged projections 4improve the non-positive connection between the roller chain 2 and thepallet received thereon. It should be noted that essentially only thefront most bottom panel 19 of a pallet received on the roller chainassembly 2 is shown in FIG. 2, while reference numeral 18 designates therearmost bottom panel, resting on the slide member 5, of the pallet justbeing removed from the shelf channel.

In order to favor a reliable running out of the pallets onto the slidemember 5, the latter one is preferably located on a slightly lower levelthan the level of the top surface of the roller chain assembly 2. In theregion of the deflection assembly 3, the jagged projections 4 of theparticular chain link member 2A release the pallet resting thereon, withthe result that the non-positive connection between pallet and rollerchain assembly 2 is released.

FIG. 3 shows a schematic perspective view of the slide member 5,together with a portion of the supporting rail 6 serving for guiding andsupporting the particular conveying means 2. Essentially, the slidemember 5 comprises two generally U-shaped profiled rail members 5.1 and5.2, which are located in a certain distance to each other such that alongitudinally extending slot is present both at the upper side and atthe lower side of that rail member assembly. In the upper regions of theprofiled rail members 5.1 and 5.2, hollow chambers 9 are provided whichare open at their front ends. These hollow members 9 serve for receivingposition indicator members 10, slidably received in that hollow chambers9, by means of which the actual position of the conveying means 2 can bevisualized. It should be noted that in FIG. 3 only the left hand sidedhollow chamber 9 is provided with a position indicator member 10.

In order to provide for an operation of the position indicator members10 under the influence of the conveying means 2, the position indicatormembers 10 are longer than the active length of the slide member 5. Theconveying means 2 is provided with driving dog members 12 adapted toshift the position indicator members 10. As driving dog members 12, forinstance permanent magnet members or friction coupling members likebrushes can be used, which are adapted to entrain the position indicatormembers 10 in both directions. The result is that the position indicatormembers 10 can take either a rest position or an operating position. Inthe operating position, the particular position indicator member 10projects out of the hollow chamber 9 through its front sided apertureand is visible through that aperture, respectively, while the particularposition indicator member 10 is hidden in the hollow chamber 9 when itis in its rest position. In order to be clearly recognizable, theposition indicator members 10 are preferably colored.

Measures are taken that different states of the particular shelf channelcan be indicated, as far as its occupation is concerned, by means of theposition indicator members 10. For instance, it can be indicated thatthe first empty chain portion is ready to receive pallets, or it can beindicated that the conveying means 2 is fully occupied. It is understoodthat also intermediate states can be indicated, for instance if several,let's say two or four position indicator members 10 per shelf channelare provided.

The driving dog members 12, together with the position indicator members10, can be designed as stop member in order to limit the forwardlydirected motion of the conveying means 2.

In order to provide for a reliable and stiff connection having a highbending resistance between the slide member 5 and the support railmember 6, the support rail member 6 is provided with grooves 7 which areadapted to cooperate with strip members 8 provided on the slide members5. In this way, it is possible to interconnect the two elements 5 and 6in a very rigid manner between two cross bar members 20 (FIG. 1).

By the provision of the longitudinal slot of the slide member 5, theconveying means 2 can be directed downwardly and deflected at thedesired position.

To sum up, it can be said that a tunnel stand bearing arrangementdesigned according to the present invention ensures a reliable andgentle deceleration of the moving conveying means 2, together with thegoods received thereon. Any danger is avoided that the goods in theshelf channel and the front most pallet, respectively, are unwillinglymoved out of the shelf channel and overrun the end of the shelf channel,respectively. This result may be achieved due to the fact that theconnection where power is transmitted by friction between the conveyingmeans 2 and the pallet 15 is released during the removal of a pallet,but before the pallet is completely removed.

I claim:
 1. Tunnel stand bearing arrangement comprising a plurality ofshelf channels, each being provided with a circulating conveying means,on which the goods to be stored are received in a frictional manner,characterized in that each shelf channel is provided with a stationaryslide member located in its end region where the goods are unloaded, theslide member having an active length corresponding to 0.8- to 1.2-timesof the mean brakeless run-out distance of the conveying means set inmotion by the removal of goods, whereby the conveyor is designed suchthat the non-positive frictional coupling between the conveying meansand the goods stored thereon is released in front of the active portionof the slide member.
 2. A tunnel stand bearing arrangement according toclaim 1, characterized in that the active length of the slide memberamounts to between 10 and 40 cm, and that the length of each of theshelf channels available for storing goods is greater than the length ofthe total effective conveying path of the conveying means.
 3. A tunnelstand bearing arrangement according to claim 1, whereby the conveyor isprovided at least in the region of the unloading end with a deflectionassembly for the conveying means, characterized in that the deflectionassembly is located in a distance from the unloading end whichcorresponds at least approximately to the active length of the slidemember.
 4. A tunnel stand bearing arrangement according to claim 1,characterized in that the conveying means is designed as circulatingchain, particularly a supporting roller chain, whereby the upper run ofthe conveying means is shorter than the length of each of the shelfchannels available for storing goods.
 5. A tunnel stand bearingarrangement according to claim 1, characterized in that a support railis provided for guiding and supporting the conveying means, the supportrail comprising longitudinal grooves adapted to cooperate withlongitudinal strip members provided on the slide member such that aninterconnection between the support rail and the slide member isrealized which comprises a high bending resistance.
 6. A tunnel standbearing arrangement according to claim 5, characterized in that theslide member comprises at least one hollow chamber which is open at itsfront end, in which a position indicator indicating the position of theconveying member is slidably received, whereby the position indicator isdesigned to cooperate with a driving dog located at the conveying means,such that the position indicator is movable between a rest position andan operating position by the particular driving dog, the positionindicator being visible when it is in its operating position.
 7. Atunnel stand bearing arrangement according to claim 6, characterized inthat the position indicator is longer than the active length of theslide member.
 8. A tunnel stand bearing arrangement according to claim6, characterized in that the driving dog together with the positionindicator constitutes a stop member for limiting the path of movement ofthe conveying means in the direction towards the unloading end of theshelf channel.
 9. A tunnel stand bearing arrangement according to claim6, characterized in that the driving dog is constituted by a permanentmagnet or a brush, whereby the latter one entrains the positionindicator by frictional engagement in both directions.
 10. A tunnelstand bearing arrangement according to claim 1, characterized in thatthe top surface of the slide member is essentially in alignment with thetop surface of the conveying means.